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From: Jeff Layton <jlayton-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>
To: Jeff Layton <jlayton-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>
Cc: "Steve French" <smfrench-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	"Björn JACKE" <bj-3ekOc4rQMZmzQB+pC5nmwQ@public.gmane.org>,
	linux-cifs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: monotonic time for mount.cifs timeouts
Date: Tue, 24 Aug 2010 14:34:33 -0400	[thread overview]
Message-ID: <20100824143433.5049ebe1@tlielax.poochiereds.net> (raw)
In-Reply-To: <20100824142248.164caebe-9yPaYZwiELC+kQycOl6kW4xkIHaj4LzF@public.gmane.org>

On Tue, 24 Aug 2010 14:22:48 -0400
Jeff Layton <jlayton-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org> wrote:

> On Tue, 24 Aug 2010 13:07:55 -0500
> Steve French <smfrench-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> 
> > Any pointers to background on gettimeofday vs
> > clock_gettime(CLOCK_MONOTONIC) and why the latter is better?
> 
> IIUC, the reason for this is that gettimeofday is affected by wallclock
> changes (think NTP):
> 
>        CLOCK_MONOTONIC
>               Clock  that  cannot  be  set and represents monotonic time since
>               some unspecified starting point.
> 
> ...so by preferring CLOCK_MONOTONIC, the mtab locking code isn't
> affected by clock jumps or skew. Bjorn, is this correct?
> 

Correction...CLOCK_MONOTONIC is affected by adjtimex(). Over a 30s
period though, that shouldn't mean much of a delta. The big danger is
large clock jumps and this should take care of that.

Out of curiousity though...did you or someone you know hit this problem
in practice, Bjorn? Or did you just notice it via inspection?

-- 
Jeff Layton <jlayton-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>

  parent reply	other threads:[~2010-08-24 18:34 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-08-24 16:16 monotonic time for mount.cifs timeouts Björn JACKE
     [not found] ` <E1OnwAo-008Rzd-Bd-dqLtpHMqGvUyWpdLl23E4A@public.gmane.org>
2010-08-24 17:34   ` Jeff Layton
     [not found]     ` <20100824133418.6319ead7-9yPaYZwiELC+kQycOl6kW4xkIHaj4LzF@public.gmane.org>
2010-08-24 18:07       ` Steve French
     [not found]         ` <AANLkTi==5ZbC7Fb8wnCea50OndXZ=QwV5xPwv19K1Fyz-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-08-24 18:22           ` Jeff Layton
     [not found]             ` <20100824142248.164caebe-9yPaYZwiELC+kQycOl6kW4xkIHaj4LzF@public.gmane.org>
2010-08-24 18:34               ` Jeff Layton [this message]
     [not found]                 ` <20100824143433.5049ebe1-9yPaYZwiELC+kQycOl6kW4xkIHaj4LzF@public.gmane.org>
2010-08-24 20:08                   ` Björn JACKE
     [not found]                     ` <E1OnznA-008e2X-Fm-dqLtpHMqGvUyWpdLl23E4A@public.gmane.org>
2010-08-24 23:30                       ` Jeff Layton
     [not found]                         ` <20100824193025.24b0f8c4-4QP7MXygkU+dMjc06nkz3ljfA9RmPOcC@public.gmane.org>
2010-08-25  0:47                           ` Steve French

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